Theodolite vs. the Total Station: Southern Photo Presents a Brief History of Surveying Equipment

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Before the advent of the electric total station, surveyors used an instrument known as a theodolite to measure angles and calculate distance. How does this purely mechanical piece of surveying equipment work and how does it compare the the electronic, computer driven total station that replaced it? Southern photo has gathered the following brief history of surveying equipment to shed some light on the differences between these two tools.

Before the advent of the electric total station, surveyors used an instrument known as a theodolite to measure angles and calculate distance. How does this purely mechanical piece of surveying equipment work and how does it compare the the electronic, computer driven total station that replaced it? Southern photo has gathered the following brief history of surveying equipment to shed some light on the differences between these two tools.

Mark Cheves, editor of The American Surveyor magazine, says that there are really only two situations in which to use a theodolite today. In the third world, where access to electricity is spotty or nonexistent, theodolites are a natural alternative to the electric-powered total station. It can do this because intead of using computer driven measurements and calculations, the theodolite employs two discs, one on the vertical and one on the horizontal plane, that are manually rotated to set an angle. The surveyor then reads the angle using a tiny microscope attached to the side of the instrument.

Also, in the construction industry, if a contractor needs to square off a building or create a simple diagonal line, a theodolite can measure a 45- or 90-degree angle fairly easily, without the added complication of using a total station with a prism and a computer.

Cheves also said there are some surveyors who like the traditional feel of a theodolite, and use it because of some closely held beliefs. In the early 1900s, before electric total stations and GPS technologies were available, surveyors had to use either a theodolite or even a compass and chain to measure angles, distances and borders. Since this was the only technology available, and state governments had to create official land boundaries for businesses and citizens, measurements taken by surveyors using these instruments were made official in governmental logs. Some highly traditional thinkers in the surveying industry, Cheves said, believe that in order to arrive at these early official borders, one must use the same instruments they had available back then.

Total station technology has assisted surveyors in several ways. One, it has eliminated human error to a large extent. With a theodolite, the surveyor must peer through a tiny microscope to see the angle, and then write it down correctly in his log book. The total station records this data, which the surveyor simply downloads onto his computer when he returns to his office.

Second, the total station has completely eliminated the need to measure lines by hand. In the past, surveyors had to use chain to mark off lines, and then count the links to measure the distance with the most accuracy. Chains are unreliable because they can lose links in transit and they change shape in very hot or cold weather, and a surveyor's goal is to get a measurement down to within a few centimeters.

Third, the total station can be set up on a tripod, allowing for a one-man surveying crew. Surveyors are difficult to come by these days. Cheves said surveying used to be a learned trade. He's been surveying since 1963 and he does not have a college degree. Now, 23 states require a four-year degree and surveyors must sit for both a national and state examination before they can work in the field. Since this is the case, many states are losing surveyors as they retire. If a company only has six people on staff, now it can send out a one-man operation.

Theodolites still have a place in the surveying industry, where electricity is sparse or when one only needs to measure a simple angle, but since the 1970s they have been almost completely replaced by the electronic total station. Old-school surveyors still keep them around, but the elimination of so much error and additional work makes the total station and GPS technology extremely attractive to surveyors today.

You can find a wide variety of total stations and other surveyors' equipment at http://www.SouthernPhoto.com?pr=042507.

About SouthernPhoto.com:
Southern Photo Inc. is a supplier of surveying equipment. We also offer repair and maintenance at our full service repair shop specializing in Topcon service and repair. In addition to surveying equipment and supplies, SouthernPhoto.com also offers drafting supplies and furniture and art supplies. For more information, visit http://www.SouthernPhoto.com?pr=042507.

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MIKE DERMATAS
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